Lymphatic Filariasis at Gomoa Okyereko, an Irrigation Project Community in Southern Ghana: Infection, Clinical Disease and Vectors

Abstract

A parasitological, clinical, periodicity and entomological study of lymphatic filariasis was earned out at Gomoa Okyereko, an irrigation project community in Southern Ghana to provide baseline information on the infection and its transmission in the community. Out of a total of 636 inhabitants, fifty percent of the residents were selected from the compiled demographic data using computer generated random numbers to constitute the study population. Quantitative examination of night blood sample (100/xl) between 21:00 and 01:00 hours from 296 (94.6%) selected persons using the counting chambers techniques (CCT) revealed high microfilarial prevalences and microfilarial geometric mean intensity (GMI) in the study group. Overall microfilarial prevalence of 26.4% was observed, and prevalence generally increased with age and was higher in females (27.6%) than in males (25%), though this was not statistically significant. Large variability was observed in individual mean intensities and an overall GMI among infected individuals was 819mf/ml of blood (1114.3mf/ml in males and 645.7mf/ml in females). There was however no statistical significance in GMI between these two sexes. Hydrocoele was the most common clinical manifestation of lymphatic filariasis and 9.3% of the male’s examination had hydrocoeles of grades 1-IV the prevalence of hydrocoele increased with age and the highest prevalence of 33.3 % was noted in 40-49 age group. Four female aged 13-55 had limb elephantiasis, two were grade I and the other two grade III. Microfilarial periodic pattern of Wuchereria bancrofti was determined in eight microfilaraemic persons. From each individual, a 100/xl finger prick blood was collected every two hours throughout one complete 24hours cycle. The peak hour (k) was calculated as 01:03 (i.e 3 minutes after 1 a.m) and the periodicity index (D) was 122.6, confirming the nocturnal periodicity of microfilariae of this parasite in Ghana. Entomological studies using pyrethrum spray collections and landing catches revealed that the species of man-biting mosquitoes in the community include Anopheles gambiae s .l, A. funestus, A. pharoensis, Culex quinquefasciatus and Mansonia species. Their relative abundance showed seasonal variation influenced by the amount of rainfall and the availability of favourable breeding places such as the irrigation canals. In the rainy season, the most abundant species was A. gambiae s .l while in the dry season, the most abundant species was A. funestus. During the period that the dam was opened, the most abundant species was A. gambiae s .l. Most of the mosquitoes were biting late in the night coinciding with the peak of microfilarial abundance in the peripheral blood. Overall infectivity rates of 7.8%, 3.9% and 9.1% were recorded for A. gambiae s .l, A. funestus, A. pharoensis respectively. A. pharoensis had a very high infectivity rate though very small numbers were collected. Other species collected in small numbers were Culex quinquefasciatus and Mansonia species and their role in the transmission of the disease was minimal. It was calculated that inhabitants in the area are at risk of getting 309.5 infective bites per man per year from A. gambiae s.l while both A. funestus and A. pharoensis may give 24.1 infective bites each. The main vector responsible for the transmission of lymphatic filariasis in the community therefore is A. gambiae s .l while A. funestus and A. pharoensis play minor roles